1. Field of the Invention
The present invention generally pertains to motor vehicles. More particular, the present invention pertains to an automatic belt tensioner for a motor vehicle.
2. Discussion
Conventional motor vehicles are provided with belts for rotatably connecting various components. In a first example, various motor vehicle accessories are powered by a continuous drive belt which is driven by an engine crankshaft through a crankshaft pulley. In a second example, a timing belt is used to synchronize engine timing and rotatably connect an engine crankshaft and cam shaft sprockets. Proper vehicle operation requires the maintenance of adequate tension in such drive belts and timing belts.
Tensioners are used to maintain proper tensioning of the drive and timing belts. Conventional tensioners include two typesxe2x80x94manual and automatic. Manual accessory belt tensioners require user action to maintain proper tension throughout the life of a belt. Automatic accessory belt tensioners typically are biased into engagement with the belt for maintaining the belt under tension.
A typical automatic belt tensioner includes a tension arm pivotally mounted on a hub. A tension pulley is rotatably attached to a free end of the tension arm. A compression coil spring biases the pulley into engagement with the belt to thereby reduce the vibration of the belt by tensioning.
Under operating conditions, when the variable load of the belt creates a force on the coil spring greater in magnitude than the biasing force of the coil spring, the pulley is displaced from its biased position against the bias of the coil spring. When the variable load of the belt subsequently falls, the belt is momentarily slackened until the coil spring can respond. This slackening of the belt often results in undesirable noise and vibrations.
Various embodiments of a belt tensioner which automatically maintains a steady tension to the drive belt of an accessory drive system are detailed in commonly assigned U.S. Ser. No. 09/442,978, filed Nov. 18, 1999. U.S. Ser. No. 09/442,978 is hereby incorporated by reference as if fully described herein.
The accessory belt tensioner of U.S. Ser. No. 09/442,978 includes a base, an arm and a tensioner pulley. The base is adapted to be fixedly interconnected to the engine. The arm is connected to the base for motion in a first direction and a second direction about an axis. The tensioner pulley is mounted on the arm and adapted to be in a contact relationship with the drive belt such that the drive belt is tightened and loosened in response to movement of the arm in the first and second directions, respectively. The accessory belt tensioner further includes a biasing arrangement and a force resisting arrangement. The biasing arrangement is carried by the base and operates to provide a biasing force to bias the arm to move in the first direction. The force resisting arrangement is carried by the base and provides a resisting force to resist movement of the arm in the second direction. The resisting force has a substantially greater magnitude than the biasing force.
In one form, the present invention provides a belt tensioner for automatically tightening a belt of a motor vehicle. The belt tensioner includes a tensioner mechanism including a hub, an inner casing and an outer casing. The outer casing is movably mounted to the inner casing. The hub is freely mounted for rotation to the outer casing and for contacting the belt and selectively tightening and loosening the belt in response to movement of the outer casing relative to the inner casing in first and second directions, respectively. The belt tensioner further includes a biasing mechanism for providing a torque force to the outer casing in the first direction. The belt tensioner additionally includes a one-way clutch mechanism normally resisting movement of the outer casing relative to the inner casing in the second direction. An exteriorly accessible rotatably member is associated with the one-way clutch mechanism for selectively deactivating the one-way clutch mechanism to prevent movement of the inner casing in the second direction.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from a reading of the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings.